1. Field of the Invention
This invention relates to a cooling structure adapted for an electronic circuit package such as an integrated circuit package, and more particularly to a cooling structure which is used to perform forced cooling of an electronic circuit package using coolant.
2. Description of the Related Art
The immersion jet cooling method is one way of cooling an integrated circuit chip which is mounted on a circuit board such as a printed circuit board and generates a high level of heat. In the immersion jet cooling method, the chip is cooled by jetting coolant from a nozzle directly to an integrated circuit chip immersed in electrical insulating liquid or to a heat sink adhered to the heat radiating face of the integrated circuit chip.
FIG. 1 shows an integrated circuit chip 201 to which a heat sink 221 is adhered. A plurality of fins 210 are formed on the heat sink 221 which extend vertically upwardly. Here, the pitch of the fins 210 is fixed. The surface of the fins 210 is finished with a smooth face or a rather rough face. The heat sink 221 is adhered to the heat radiating face of the integrated circuit chip 201 by means of a heat conducting bonding member 202. The heat conducting bonding member 202 may be, for example, solder or a resin bonding agent having a high heat conductivity.
The application of the immersion jet cooling method to an integrated circuit chip 201 to which a heat sink 221 is adhered in this manner is performed in the following manner. As shown in FIG. 2, one or a plurality of integrated circuit chips 201 are disposed on a circuit board 206. A pipe 205 is provided in an opposing relationship to the circuit board 206. Coolant circulates in the inside of the pipe 205, and nozzles 209 for jetting coolant therethrough are provided on the face of the pipe 205 opposing the circuit board 206. The nozzles 209 are disposed at locations corresponding to the integrated circuit chips 201.
An upper end portion of the heat sink 221, that is, an end portion of the heat sink 221 adjacent the pipe 205 is open between adjacent fins 210. Consequently, coolant jetted from the nozzles 209 passes the gaps between the fins 210 and reaches the interior of the gaps in such a manner that it collides with the portions of the heat sinks 221 corresponding to the central portions of the integrated circuit chips 201. The coolant then flows out from the side portions of the fins 210 or the upper ends of the heat sinks 221. An electrically insulating liquid having a low boiling point is normally used as the coolant. Here, the liquid having a low boiling point represents a liquid having a boiling point lower than the surface temperature of the electronic circuit package during operation. Since a liquid having a low boiling point is used as the coolant, part of the coolant that has come in contact with the fins 210 or heat sinks 221 will boil and evaporate, and cooling is performed efficiently by the heat of vaporization.
In the arrangement shown in FIGS. 1 and 2, since the fins 210 are provided, coolant jetted from the nozzles 209 flows as indicated by the arrow marks in FIG. 2 and can remove, at the positions corresponding to the central portions of the integrated circuit chips 201, air bubbles produced on the surfaces of the fins 210 as a result of boiling. However, at peripheral portions of the integrated circuit chips 201, the flow of coolant is obstructed by the fins 210 provided at the central positions, and the cooling efficiency or the cooling rate cannot be enhanced compared with the central portions. Consequently, the surface temperature of each integrated circuit chip 201 will vary between the central portion and peripheral portion of the chip, and a sufficient cooling effect will not always be obtained as a whole.
The necessary amount of coolant increases in proportion to the power dissipation of the integrated circuit chip. Therefore, when the amount of heat generation per unit area increases with a circuit board on which an integrated circuit chip is mounted, the capacity of the coolant supply apparatus and/or the size of the pipe system for coolant must be increased, and the amount of coolant itself must also be increased.
U.S. Pat. No. 4,590,538 to Cray discloses a technique by which a plurality of stacks of circuit modules are arranged in a generally radial pattern to form a columnar aggregate and the aggregate is accommodated in a container to cool the circuit modules by means of coolant. According to the method by Cray, coolant is supplied along the center axis of the column so as to form flows of coolant in radial directions which perform forced cooling of the circuit modules.
When an electronic circuit module is cooled using any of the methods described above, the circuit board and the integrated circuit chip or chips and the heat sink on the circuit board are all immersed in coolant. Consequently, the cooling efficiency is not high. And when the circuit board or the integrated circuit chip or chips must be exchanged, the disassembling and assembling operations are complicated.